Removal of antibiotics by an integrated process coupling photocatalysis and biological treatment – Case of tetracycline and tylosin

Much attention has been recently devoted to the fate of pharmaceutically active compounds such as antibiotics in soil and water. Among them, tetracycline (TC) and tylosin (TYL) antibiotics were shown to be poorly biodegradable and toxic for microorganisms. The question of their fate in the environment has to be clearly identified in order to prevent any environmental contamination and to avoid generating antibioresistant strains. Hybrid processes involving a physico-chemical pre-treatment like photocatalysis coupled to a biological treatment have been considered for their removal. Prior to a biological treatment, pre-treatment of both antibiotics by photocatalysis was considered in this work. To ensure a significant residual organic content for the biological treatment, an irradiation time of 2 h was considered. A decrease of the residual amount of antibiotics contained in the irradiated solutions was recorded, which can be related to an “inherent” biodegradation since these residual concentrations were below their inhibitory thresholds, 18 and 9 mg l−1 for TC and TYL. The absence of biodegradability of TC by-products was noted because of their toxicity (EC50 < 1%) while TYL by-products showed a significant biodegradability (56% COD decrease). TYL toxicity decreased from highly toxic (EC50 < 1%) initially to toxic (EC50 = 36%) after irradiation.

► Tetracycline and tylosin antibiotics are non-biodegradable and toxic for microorganisms.
► Photocatalysis coupled to a biological treatment have been considered for their removal.
► To ensure a significant residual organic content 2 h irradiation time was considered.
► Tetracycline by-products were not biodegradable and toxic.
► After an acclimation time, tylosin by-products were significantly biodegradable.